Electric vehicles typically utilize an electric motor to provide for traction that provides horizontal movement of the vehicle. Batteries installed on the electric vehicle provide the electric motor with a source of electrical energy. The electric vehicle and associated motor or motors may be configured to operate using either an AC (alternating current) or DC (direct current) electrical system. A rate of energy discharge from the battery during operation of the vehicle depends on a number of conditions including vehicle travel speed, weight of load being transported, efficiency of the electrical system, and even operating temperatures, among others.
The overall productivity of an electric vehicle is limited by an amount of energy that is stored in the vehicle battery. Where the electric vehicle is operated for extended or multiple shifts, the battery typically needs to be recharged or replaced one or more times. This results in lost productivity time, and requires that charged replacement batteries are stocked and made available. Manufacturers of these vehicles have typically responded to these demands by increasing the size, and hence capacity, of these batteries. However, the increased size of the battery reduces vehicle performance and effective operating time due to the increased weight, and adds cost to the battery and vehicle purchase price. Furthermore, many vehicle operations place a premium on vehicle operating space, such that any increase in battery size is limited by the maximum allowable battery compartment space available.
With the advent of regenerative traction systems, electric vehicle manufacturers have designed electrical systems that are configured to regenerate electricity when the vehicle is decelerated or braked. The battery is partially recharged with regenerated energy that is delivered by the electric motor and a power circuit. In this case, the electric motor may operate as a generator to generate the regenerated electricity.
Typically, these regenerative braking systems include a lead acid battery. However, there are limits inherent in the chemical processes involved in charging a lead acid battery. As a result, a lead acid battery cannot change from discharging to recharging fast enough and accept a high enough rate of recharge to recover a high percentage of regenerative energy. Using the motor as a generator results in bursts of energy that tend to exceed the rate at which the battery may be recharged effectively. Further, the ability of a lead acid battery to absorb energy is inversely proportional to its state of charge. That is to say, the greater the existing charge on the battery, the lower the rate at which it can accept incoming energy during the recharging event. A nearly fully charged battery, such as at the beginning of a shift, is particularly inefficient at absorbing the incoming energy during regenerative braking. Energy not recaptured by charging the battery is dissipated as heat.
The present invention addresses these and other problems.